Exhaust Manifold Bolt Holes Stripped in Head

[sheppjr]

My 78 TR7 FHC had an exhaust leak between the manifold and head. I got the bright idea to add gaskets between the manifold and the head to seal the leak as was done on FI cars. When I removed the bolts securing the manifold, every one of the bolts stripped out during removal. Aluminum was embedded in the threads of the bolts. I have tried longer bolts hoping there was enough thread left in the head, but the bolts will not tighten to the specified torque value in the factory Manual.

Since the manifold is still leaking, I believe the only option is to helicoil all seven stripped out holes in the head. Has anyone done this with the engine in the car or will engine removal be required? I do not want to pull the head for obvious reasons and would rather lift the engine if I have no other options. Can you helicoil the top front and top rear bolt holes? These holes are drilled through a flange.

I have a right angle drill and believe that the job can be done but have not been able to source a 25/64 machine screw drill bit with a 3/8 shank. WW Grainger has 25/64 drill bits but I will have to get one and have the shank turned down to fit my drill.

The odd thing is the Manual says that the manifold is secured with 3/8" UNF bolts. The ones I pulled out look like UNC. Is the Manual right or did a DPO cause my problem by using the wrong bolts years ago?

Any advise will be much appreciated.

Richard Sheppard

[Hasbeen]

Richard, my 80 FHC has course thread blots on the manifold, so it is
probably a common problem.
Mine are not helicoils, so I believe they have been tapped out to
take what look like larger bolts.

I think this is a better idea, as I have not had much success with
helicoils in alloy, & you should be able to easily get the drill to
suit the thread taps you chose.

I use a smear of the orange, high heat silicon on the head to
manifold, & manifold flange joints on 7s. It is the only place I
would use silicon as a gasket, It workes well, & can't get into
anywhere from there, to cause any trouble, like it does in oil, or
water ways.

Hasbeen

[FI Spyder]

My rear manifold bolt was missing altogether so it was leaking past the rear gasket which was skewed slightly so you couldn't get the bolt in without tapping the hole. You couldn't hear it but there was muck that leaked out and discoloured the head. I believe it came this way from the factory, if the bolt just dropped out it was still so tight the gasket wouldn't have skewed. The bolt was 3/8" UNF although just looking at I would have guessed UNC. Must be the angle of everything.

TR7 Spider - 1978 Spifire - 1976 Spitfire - 1988 Tercel 4X4 - Kali on Integra - 1991 Integra

[Beans]

If the thread is more or less completely removed already it should be no problem to tap the helicoil thread directly into the head without drilling out the holes first.

As for the original bolts, UNF and UNC says something about thread pitch and this is very much related to the bolts diameter.
Have to agree original; manifold bolts look like they are UNC

<center>
<font color="blue"><i>1981 TR7 FHC Sprint (better known as 't Kreng)
1981 TR7 DHC (not very well known yet, but back on the road)
Also a 1980 TR7 DHC, 1980 TR7 DHC FI, 1981 TR7 FHC
http://tr7beans.blogspot.com/</i></font id="blue"></center>

[John Clancy]

Robsport's tip for this is to put a bolt in with a slightly different thread - an M8 if memory serves correctly. I had exactly this problem a couple of times and I can confirm that their tip works. The new bolt with the different screw thread cuts its own thread into the aluminium.

The problem with the cylinder head to exhaust manifold is the aluminium is so prone to warping due to the heat. This and the weak threads in the head itself. I've just had the head skimmed along the faces where it meets the exhaust. Will it last? I doubt it but at least all the gases are sealed for the moment. Had new screw threads welded in for the four bottom bolts as well so I think I've thrown everything at this known problem area. Already modified the three top bolts to take a nut and a bolt years ago.

<center><b>[url="http://www.triumphtr7.com/documents/sales/codenamebullet.asp"]Buy the story of the Triumph TR7/8 on DVD here[/url]</b></center>

[Wayne S]

I had this exact same problem with mine and spent 2 years solving it before giving in and finally changing the head.

The big warning really is that the Repair Operation Manuals all state that the bolts are 3/8 UNF ... BUT THEY ARE DEFINATELY 3/8 UNC with a threaded section exactly 1" in length. My car was maintained by countless garages before my ownership and the history file shows it had been in many times with leaking manifold problems, with each garage trying defferent threaded bolts before it screwed the threads up beyond repair.
I had fited helicoils myself by getting under the car and doing them from there. Only required in the bottom holes as you can nut and bolt the top ones. It is possible but they didint last too well. I had a rubber exhaust mount snap and this caused 2 of the insert helicoils to snap.
Head removal wasnt as traumatic as I imagined it would be and its a good excuse to have it ported and flowed etc. I now enjoy the sweet sound of a sealed manifold to head joint [8D]

Purple 2.0 Litre DHC Grinnal

[bmcecosse]

Screw Threads in aluminium should always be 'course' - ie 3/8" UNC. Possibly the outer end of each stud is 3/8" unf - to take normal fine threaded nuts.
It may be possible to re-tap the threads in the head to take 10mm studs.

[sheppjr]

Thanks for all the replies! All of your suggestions are worthy of consideration. I have already gone the bolt and nut route on the top front and rear mounting holes. The Robsport suggestion is most interesting as it appears to be the easiest to do. However, I am worried that this is a temporary fix. Is the diameter of the M8 bolt sufficent to cut deep enough threads so that the bolt can be removed in the future without having the same problem? Why not run an M8 tap into the holes to cut the threads as opposed to the bolt? Going with the next size bolt on the lowers and/or just tapping the holes is also appealing. I assume the next size is 7/16 x 14?

Thanks again for all the suggstions. I will let you guys know how this ends up.

Richard Sheppard

[bmcecosse]

M8 is smaller than 3/8" - so won't do at all. Need to be 10mm to have any success. But do use a tap in the hole - don't just try to screw into the aly.

[john 215]

Hi,
If you do go the helicoil route,why not fit studs instead of bolts[?]that way no danger of cross threading or such like whilst holding a cast iron manifold in one hand,a bolt in the other and another bolt in your mouth,we have all been there[:D]
I once replaced a partially damaged manifold bolt hole with a witworth bolt as this had a slightly different pitch (a lot more coarse than metric),but then they are not available from your local Hellfords.
Cheers John.

LIVE LIFE A QUARTER OF A MILE AT A TIME!
1979 3.5 FHC(STATUS PENDING!!)

1982 2.0 DHC Soon to be a 4.6 fire breather!!
Read My Blog http://www.waringstowntr7s.co.uk/blogs/ ... hp/John215

[sheppjr]

bmcecosse,

You are correct, the M8 is too small. I think the best options are to either retap the holes for M10-1.50 bolts or use M10-1.50 studs and nuts. I compared the M10 tap with a 3/8 x 16 tap and I should be able to run the tap into the hole without having to drill the holes out. My plan is to try this in the top front hole first since it has the easiest access. Hopefully I can pull the manifold sometime this week.

Richard

[FI Spyder]

All FI engines came with exhaust manifold gaskets, carb engines didn't but it is recommended to use them in carb versions when manifold is being reinstalled. Makes sense to me. You've got to get a better seal.

TR7 Spider - 1978 Spifire - 1976 Spitfire - 1988 Tercel 4X4 - Kali on Integra - 1991 Integra

[bmcecosse]

Seriously - no ex manifold gasket ??

[Beans]

Yess ... TR7's on carbs didn't have gaskets between exhaust manifold and head. On the other hand, in 19 years of TR7 motoring that's never been a problem...

<center>
<font color="blue"><i>1981 TR7 FHC Sprint (better known as 't Kreng)
1981 TR7 DHC (not very well known yet, but back on the road)
Also a 1980 TR7 DHC, 1980 TR7 DHC FI, 1981 TR7 FHC
http://tr7beans.blogspot.com/</i></font id="blue"></center>

[john 215]

Hi,
As Beans said i too never had a problem,except when i put a four branch on,then a complete b1tch to seal ended up cutting rewelding and fitting FI gaskets,that was 17 od years ago so hopefully they may have improved or at least use a jig to weld them up!!
On the subject of no gaskets on exhaust manifolds,the 2.3/2.6 SD1 never had any either never saw a manifold blow,just hundreds of head gasket [}:)]
Chers John.

LIVE LIFE A QUARTER OF A MILE AT A TIME!
1979 3.5 FHC(STATUS PENDING!!)

1982 2.0 DHC Soon to be a 4.6 fire breather!!
Read My Blog http://www.waringstowntr7s.co.uk/blogs/ ... hp/John215